With developments of mobile communication, there are various types and materials developed for mobile terminals, especially for mobile phones. Recently, it has become increasingly popular to design the rear cover as metal shells because of the favorable appearance and good touching feel of the metal shell and the better wear-resistance compared with plastic shells such as polycarbonate (PC) or acrylonitrile butadiene styrene copolymer (ABS) shells.
At present, the main types of antenna for mobile terminals, particularly for mobile phones, are a planar inverted-F antenna (PIFA), an inverted-F antenna (IFA), a unipolar antenna and a loop antenna. However, these antennas could not efficiently send or receive electromagnetic signals when applied on a mobile terminal having a metal shell.